1. Field of the Invention
The present invention relates to a carburetor, with a choke including an air control valve, for an internal combustion motor.
2. Description of the Prior Art
In a large number of carburetors actually in use, the "choke" for cold starting is made up of a mechanism comprising a choke handle, and a choke valve rotatably mounted in the carburetor body above the fuel nozzle. When one pulls the choke handle, the choke valve completely closes and blocks air from entering the body of the carburetor. When the motor turns over, a diaphragm having one side connected to the intake manifold opens the choke valve halfway as a result of the low pressure then prevailing in the intake manifold due to the small butterfly gas valve opening. After starting the engine, the choke is partially closed as the engine runs cold. The effect of this is to place the choke valve in an intermediate, half open position between its closed and fully open positions.
Of course, fully or partially closing the air valve enriches the air-fuel mixture reaching the engine. This enrichment increases proportionally as the air valve is closed further.
As a result, automobiles equipped with such carburetors consume excess fuel when cold. This over-consumption is increasingly significant the colder the engine is. As shown in FIG. 9 of the attached drawings, curve A represents, as a function of distance travelled, the fuel consumption (in liters/100 km) of an engine after a cold start at an ambient temperature of -5.degree. C., and curve C illustrates the fuel consumption of the same engine after a warm start.
However, statistical studies have shown that a large number of vehicles, notably in an urban setting, were used for daily trips of a few kilometers, i.e. in the least favorable section of Curve A. Substantial fuel savings could be realized if one were to reduce cold-running over-consumption of a large number of vehicles by equipping them with revised choke valve carburetors.
The French Pat. No. 2 393 161 describes a carburetor which helps solve this problem. This carburetor is of the type consisting of a body provided with a fuel nozzle, a choke valve rotatably mounted in the body above a fuel nozzle device, a butterfly valve which controls the engine load, rotatably mounted in the body below the fuel nozzle device, a spring that pulls the air valve back into its fully closed position, a valve activating device that is sensitive to the low pressure prevailing in the intake manifold and a connecting linkage between the low pressure sensitive device and the choke valve, the linkage having at least one articulation. The low pressure sensitive activating device is disposed so as to allow the choke valve to pivot between its fully closed position and a position of maximum opening against the spring force. A manually operated cam is rotatably mounted between a first position, corresponding to cold starting, where it interacts with the linkage to limit the opening movement of the choke valve to a partial open position, a second position, corresponding to cold running, where it allows the choke valve to pivot between a minimum opening position and said maximum opening position and a third position where it holds the choke valve in a fully open position.
However, the structure of this carburetor is relatively complex and it is costly to produce because it consists of a large number of different interrelating moving parts. The present invention contemplates a carburetor of the above type whose construction is particularly simple.